Polymerase Chain Reaction

Polymerase chain reaction (PCR) uses an enzyme known as polymerase to rapidly multiply a small fragment of deoxyribonucleic acid (DNA)—a double-stranded, ladderlike molecule that carries the hereditary material in all living things. Each cycle of PCR consists of three phases. In the first phase, denaturation, the DNA is heated to cause its two linked strands to separate. In the second phase, annealing, the temperature of the mixture is lowered to allow primers—starter pieces of DNA—to bind to the separated DNA. In the third phase, polymerization, the temperature is raised to allow the polymerase enzyme to rapidly copy the DNA. Each PCR cycle duplicates the existing DNA, so over 1 billion copies of a single DNA fragment can be made in just a few hours.